Numerous disease states could benefit from the modification of subject respiration, including heart failure, sleep disordered breathing (e.g., sleep apnea, etc.) and other sleep disorders (e.g., snoring), hypertension, chronic obstructive pulmonary disease (COPD), bronchitis, asthma, and many others.
Heart failure, or congestive heart failure (CHF), is a common clinical syndrome that represents the end-stage of a number of pulmonary and cardiac disease states. Heart failure is a degenerative condition that occurs when the heart muscle weakens and the ventricle no longer contracts normally. The heart can then no longer adequately pump blood to the body including the lungs. This may lead to exercise intolerance, or may cause fluid retention with subsequent shortness of breath or swelling of the feet. Over four million people are diagnosed with heart failure in the United States alone. Morbidity and mortality in subjects with heart failure is high.
Sleep apnea is one form of sleep disordered breathing. Sleep apnea is defined as the temporary absence or cessation of breathing during sleep. Airflow must be absent for some period of time longer than the usual inter-breath interval, typically defined as ten seconds for adults and eight seconds (or more than two times the normal respiratory cycle time) for infants. There are several general varieties of sleep apnea: central, obstructive, complex, and mixed. In central sleep apnea, the subject makes no effort to breathe. In obstructive apnea, ventilatory effort is present, but no airflow results, because of upper airway closure. In mixed apnea, there is initially no ventilatory effort (suggestive of central sleep apnea), but an obstructive sleep apnea pattern becomes evident when ventilatory effort resumes. Finally, hypopnea is a temporary decrease in inspiratory airflow relative to the previous several inspirations. The terms sleep apnea and/or sleep disordered breathing may refer to hypopnea.
Hypertension refers to elevated blood pressure, and is a very common disease. Hypertension is characterized by elevated systolic and/or diastolic blood pressures. Despite the prevalence of hypertension and its associated complications, control of the disease is far from adequate. Only a third of people with hypertension control their blood pressure adequately. This failure reflects the inherent problem of maintaining long-term therapy for a usually asymptomatic condition, particularly when the therapy may interfere with the subject's quality of life, and when the immediate benefits of the therapy are not obvious to the subject.
Chronic obstructive pulmonary disease (COPD) includes chronic bronchitis, emphysema and asthma. In both chronic bronchitis and emphysema, airflow obstruction limits the subject's airflow during exhalation. COPD is a progressive disease characterized by a worsening baseline respiratory status over a period of many years with sporadic exacerbations often requiring hospitalization. Early symptoms include increased sputum production and sporadic acute exacerbations characterized by increased cough, purulent sputum, wheezing, dyspnea, and fever. As the disease progresses, the acute exacerbations become more frequent. Late in the course of the disease, the subject may develop hypercapnia, hypoxemia, erythrocytosis, cor pulmonale with right-sided heart failure, and edema.
Chronic bronchitis is characterized by a chronic cough with sputum production leading to obstructed expiration. Pathologically, there may be mucosal and submucosal edema and inflammation and an increase in the number and size of mucus glands. Emphysema is characterized by destruction of the lung parenchyma leading to loss of elastic recoil, reduced tethering of airways, and obstruction to expiration. Pathologically, the distal airspaces are enlarged.
Asthma is another chronic lung condition, characterized by difficulty in breathing. People with asthma have extra-sensitive or hyper-responsive airways. The airways react by obstructing or narrowing when they become inflamed or irritated. This makes it difficult for the air to move in and out of the airways, leading to respiratory distress. This narrowing or obstruction can lead to coughing, wheezing, shortness of breath, and/or chest tightness. In some cases, asthma may be life threatening.
In all of these diseases, current medical and surgical therapies are not completely effective, and there is considerable room for improvement. Two therapies that are used to treat these diseases are pulmonary rehabilitation (including pursed-lip breathing) and non-invasive mechanical ventilation.
Pulmonary rehabilitation is frequently used to treat subjects suffering from a variety of medical ailments such as those mentioned. For example, COPD subjects are taught new breathing techniques that reduce hyperinflation of the lungs and relieve expiratory airflow obstruction. One of the goals of this training is to reduce the level of dyspnea. Typically, these new breathing techniques include diaphragmatic and pursed-lip breathing. Pursed-lip breathing involves inhaling slowly through the nose and exhaling through pursed-lips (as if one were whistling), taking two or three times as long to exhale as to inhale. Most COPD subjects instinctively learn how to perform pursed-lip breathing in order to relieve their dyspnea. Moreover, subjects with asthma and other respiratory ailments, and even normal people during exercise, have been shown to use pursed-lip breathing, especially during times of exertion.
It is widely believed that producing a proximal obstruction (e.g., pursing the lips) splints open the distal airways that have lost their tethering in certain disease states. In other words, airways that would normally collapse during respiration remain open when the subject breathes through pursed-lips. Moreover, by increasing exhalation time, respiratory rate can be reduced and, in some cases, made more regular.
The medical literature has confirmed the utility of pursed-lip breathing in COPD subjects. Specifically, it has been found that pursed-lip breathing by COPD subjects results in a reduction in respiratory rate, an increase in tidal volumes, and an improvement of oxygen saturation. All of these effects contribute to a reduction in subject dyspnea. However, pursed-lip breathing requires conscious effort. Thus, the subject cannot breathe through pursed-lips while sleeping. As a result, the subject can still become hypoxic at night and may develop pulmonary hypertension and other sequelae as a result. Furthermore, the subject has to constantly regulate his own breathing. This interferes with his performing of other activities because the subject must pay attention to maintaining pursed-lip breathing.
Non-invasive positive pressure ventilation (NPPV) is another method of treating diseases that benefit from regulation of the subject's respiration. NPPV refers to ventilation delivered by a nasal mask, nasal prongs/pillows or face mask. NPPV eliminates the need for intubation or tracheostomy. Outpatient methods of delivering NPPV include bilevel positive airway pressure (BIPAP or bilevel) ventilator devices, or continuous positive airway pressure (CPAP) devices.
NPPV can deliver a set pressure during each respiratory cycle, with the possibility of additional inspiratory pressure support in the case of bi-level devices. NPPV has been shown to be very efficacious in such diseases as sleep apnea, heart failure, and COPD, and has become increasingly used in recent years. Many subjects use CPAP or BIPAP at night while they are sleeping.
However, most subjects experience difficulty adapting to nocturnal NPPV, leading to poor compliance. Mask discomfort is a very common problem for subjects new to NPPV, because of the high pressures on the nose, mouth, and face, and because of uncomfortably tight straps. Nasal congestion and dryness are also common complaints that may vary by season. The nasal bridge can become red or ulcerated due to excessive mask tension. Eye irritation and acne can also result. Still other subjects experience abdominal distention and flatulence. Finally, air leakage through the mouth is also very common in nasal NPPV subjects, potentially leading to sleep arousals.
Both pursed-lip breathing and the use of NPPV have been shown to offer significant clinical benefits to subjects with a variety of medical illnesses, including but not limited to COPD, heart failure, pulmonary edema, sleep apnea (both central and obstructive) and other sleep disordered breathing, cystic fibrosis, asthma, cardiac valve disease, arrhythmias, anxiety, and snoring. Expiratory resistance is believed to provide the bulk of clinical improvements when using pursed-lip breathing and NPPV, through a variety of physiologic mechanisms. In contrast, inspiratory support is not believed to offer clinical benefits in many subjects. For example, in COPD, expiratory resistance facilitates expiration, increases tidal volume, decreases respiratory rate, and improves gas exchange. In the case of heart failure, it is felt that positive pressure in the airways (due to expiratory resistance) reduces pulmonary edema and improves lung compliance, decreases preload and afterload, increases pO2, and decreases pCO2. In many disease states, expiratory resistance helps maintain a more stable respiratory rate that can have profound clinical effects to the subject.
It would therefore be desirable to have a medical device and/or procedure that mimics the effect of pursed-lip breathing and/or the benefits of non-invasive ventilation without suffering from the drawbacks described above.
General respiratory devices addressing many of these problems may be found in U.S. patent application Ser. No. 11/298,640, filed Dec. 8, 2005, herein incorporated by reference in its entirety. Described herein are respiratory devices and methods of using them that include many features not previously developed or described.